docs: archive MVP design-qa record and refresh doc indexes

- Move root design-qa.md → docs/archive/2026-07-mvp-delivery/ (MVP-phase
  screenshot QA, concluded passed; register in archive README)
- Rename 20260708 UUID screenshot to descriptive name
- Index the 2026-07-08 integration plan in README, docs/README, AGENTS.md

AGENTS.md

@@ -82,6 +82,7 @@
 - 阶段交付归档：`docs/archive/2026-07-mvp-delivery/`
 - 分阶段总纲：`docs/银城员工端APP分阶段实施总纲.md`
 - AI 陪练二期推进（阶段一执行）：`docs/AI陪练二期开发推进计划.md`
+- 数字师傅产品定案（2026-07-08 学练问报/问题榜/学分）：`docs/20260708/数字师傅学练问报整合方案.md`
 - AI 陪练缺口修订：`docs/AI陪练功能优化与缺口分析(修订).md`
 - 后端 API 对接：`docs/API_INTEGRATION.md`
 - 对外会议版口径：`docs/AI人力资源系统项目规划方案与AI接口说明.md`